In heterogeneous chemical reactions the chemical reaction is often catalysed by solid catalyst particles. These catalyst particles are typically located in catalyst beds, and during passage of a reactive fluid through the catalyst bed, a chemical reaction takes place, thereby converting the reactive fluid into the desired product or mixture of products having a chemical composition different from that of the reactive fluid.
The inner contents of a reactor are known as reactor internals. The catalyst bed is kept in position in the reactor by reactor internals which allow fluid passage to and from the catalyst particles. This is commonly done by perforating the reactor internals in contact with the catalyst particles. The nature of the perforation determines the fluid flow pattern inside the catalyst bed.
The reactor internals for keeping the catalyst bed in position are typically a catalyst support plate supported along its edges and/or on the free side opposite the catalyst side. In some cases it is not feasible to support the catalyst support plate on this free side, as for example is the case when the catalyst particles and the catalyst support plate undergo large movement due to thermal expansion of the internals.
The catalyst bed can typically have a free upper surface and a bottom surface supported by a horizontal catalyst support plate with perforations. The catalyst bed is kept in place by the vertical non-perforated walls of the catalyst housing and by the perforated catalyst support plate. Gas then enters the catalyst bed from the free upper surface side and leaves the catalyst bed through the perforated catalyst support plate at the bottom of the catalyst bed. The catalyst support plate is fixed along its edge to the vertical catalyst housing wall and is typically not supported on its free side from below. When the reactor is heated up, thermal expansion of the catalyst bed and the vertical walls of the catalyst housing or other reactor internals cause a deformation of the catalyst bed and the reactor internals in a downward axial direction.
During passage of the reactive fluid across the catalyst bed and catalyst support plate, the reactive fluid experiences a pressure drop and this, combined with the weight of the catalyst particles on the catalyst plate, can cause deformation of the catalyst support plate. There exists therefore an upper limit for the surface area of the support plate when the catalyst support plate is only supported along its edges. Proceeding above this upper limit would demand an impractical or uneconomical reinforcement of the catalyst support plate for instance the use of a very thick catalyst support plate.
An alternative method of supporting the catalyst support plate is by using various supporting structures placed in the catalyst bed and fixed on the catalyst support plate. This allows the use of larger catalyst support plates in comparison to fixing the support plate to the catalyst housing walls. Supporting structures such as stays fixed on the catalyst support plate can be used. Stays are supportive elements fixed at one end to a first structure and at its other end to a second structure, providing support to one or both of the structures.
However, stays and such similar supporting structures can have differences in thermal expansion due to unequal temperature distribution in the reactor. This causes high stress effects within the catalyst support plate and in the stays in the axial direction, and this can lead to their deformation or rupture. The forces experienced by these particular reactor internals in the radial direction are negligible compared to the forces in the axial direction.
The English abstract of JP patent application No. 49010172 discloses a catalytic reaction apparatus useful in high temperature catalytic reactions for avoiding rupture of the catalyst supporting plate. The catalyst supporting plate has holes and is partitioned into one or more regions and a supporter for the catalyst-supporting plate. Both are fastened with vertical bolts. The thermal expansion of the catalyst supporting plate can be absorbed by loosening the bolts between the plate and its supporter so that they can slide relative to each other.
This application describes a catalytic reaction apparatus in which the stresses in the catalyst supporting plate are reduced in the radial direction only. There is no mention of how to reduce the stresses in the axial direction. It is therefore an objective of the invention to provide a catalytic reactor in which thermal stresses on the reactor internals in the axial direction are reduced. This in turn reduces deformation and rupture of the reactor internals.